The requirements of electronic detection and surveillance systems using low temperature solid state devices has led to a new class of cooling systems. They differ from previous systems primarily in the small amount of heat transported to obtain a considerable temperature differential, e.g. ambient to liquid nitrogen temperatures. In early devices the cooling was, in fact, achieved by adding liquid nitrogen through a system of dewars, the liquid being produced by a remote processing plant. The logistics involved in supporting such a system, at least in military situations, soon becomes prohibitive.
Since thermoelectric coolers do not provide the necessary temperatures and efficiencies, the latest systems generally employ cryogenic coolers like the Stirling cycle devices, i.e. closed systems with compressors and regenerators. The most practical compressor currently available appears to be the type using a cylinder enclosing a moving piston; the latter being driven by a crankshaft, through connecting rods, in a conventional manner well known in the art. These devices perform efficiently, and when driven by an electric motor sealed into the system, have extremely long lifetimes.
One drawback of these systems is that they produce considerable noise and vibration. This is particularly true of single cylinder compressors which are most desired for portable electro-optical systems, because of their small size and weight. Two cylinder arrangements can be balanced, but even these can become unbalanced as the components of one cylinder wears more than the other. The noise problem is important in military and similar roles where the devices are often used in covert operations.